Tektro RL721 and Tiagra STI brake levers

I've read couple of posts about how hard is to setup the brakes in such a way that the STI brake levers won't bottom out.
What is very weird is that the front break works great. No matter how harder I brake I cannot bottom out the STI lever.
The R break is different. I put the pads 1-2 mm away from the rim but still can bottom out the STI lever. Increased the tension in cable as much as I could. Yes it breaks but not like the front break. By the way the short tektro lever works perfect, you just press a little and it brakes very strong. I'm used to the STI break style though. Basically the tektro lever is too tight and the sti lever is to soft. Using the barrel adjuster on the Tektro lever didn't help much. Maybe the cable that goes to tektro is too short or the one that goes to the STI too long.
How can I improve that? Why the F break works better? Is it something that can be done with the STI break lever to adjust it?
I was thinking for tonight to try something out. Adjust the barrel on the top mount lever to the lower position so would loose the lever and then remove 1 pad adjustment from each brake and then re-tension the cable break so it would close again the pads to the rims. What do you think guys? Hopefully the top mount lever would allow me to do that.

Could be the rear brake cable housing is compressing. You could get better housing (jagwire is nice), or decrease the mechanical advantage on your brakes by increasing the length of the straddle cable.